Module: ActiveRecord::Acts::Tree::ClassMethods

Defined in:
lib/active_record/acts/tree.rb

Overview

Specify this acts_as extension if you want to model a tree structure by providing a parent association and a children association. This requires that you have a foreign key column, which by default is called parent_id.

class Category < ActiveRecord::Base
acts_as_tree :order => "name"
end

Example:
root
\_ child1
    \_ subchild1
    \_ subchild2

root      = Category.create("name" => "root")
child1    = root.children.create("name" => "child1")
subchild1 = child1.children.create("name" => "subchild1")

root.parent   # => nil
child1.parent # => root
root.children # => [child1]
root.children.first.children.first # => subchild1

In addition to the parent and children associations, the following instance methods are added to the class after calling acts_as_tree:

  • siblings - Returns all the children of the parent, excluding the current node ([subchild2] when called on subchild1)
  • self_and_siblings - Returns all the children of the parent, including the current node ([subchild1, subchild2] when called on subchild1)
  • ancestors - Returns all the ancestors of the current node ([child1, root] when called on subchild2)
  • root - Returns the root of the current node (root when called on subchild2)
  • descendants - Returns a flat list of the descendants of the current node ([child1, subchild1, subchild2] when called on root)

Instance Method Summary collapse

Instance Method Details

#acts_as_tree(options = {}) ⇒ Object

Configuration options are:

  • foreign_key - specifies the column name to use for tracking of the tree (default: parent_id)
  • order - makes it possible to sort the children according to this SQL snippet.
  • counter_cache - keeps a count in a children_count column if set to true (default: false).


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# File 'lib/active_record/acts/tree.rb', line 43

def acts_as_tree(options = {})
  configuration = {
    :foreign_key => "parent_id",
    :order => nil,
    :counter_cache => nil,
    :dependent => :destroy,
    :touch => false
  }
  configuration.update(options) if options.is_a?(Hash)
  
  # facebooker seems unhappy with :touch
  if configuration[:touch]
    belongs_to :parent,
               :class_name => name,
               :foreign_key => configuration[:foreign_key],
               :counter_cache => configuration[:counter_cache],
               :touch => configuration[:touch]
  else
    belongs_to :parent,
               :class_name => name,
               :foreign_key => configuration[:foreign_key],
               :counter_cache => configuration[:counter_cache]
  end
  
  has_many :children,
           :class_name => name,
           :foreign_key => configuration[:foreign_key],
           :order => configuration[:order],
           :dependent => configuration[:dependent]
  
  class_eval <<-EOV
    include ActiveRecord::Acts::Tree::InstanceMethods
    
    scope       :roots,
                :conditions => "#{configuration[:foreign_key]} IS NULL",
                :order => #{configuration[:order].nil? ? "nil" : %Q{"#{configuration[:order]}"}}
    
    after_save :update_level_cache
    after_update :update_parents_counter_cache
    
    def self.root
      roots.first
    end
    
    def self.childless
      nodes = []
      
      find(:all).each do |node|
        nodes << node if node.children.empty?
      end
      
      nodes
    end
    
    validates_each "#{configuration[:foreign_key]}" do |record, attr, value|
      if value
        if record.id == value
          record.errors.add attr, "cannot be it's own id"
        elsif record.descendants.map {|c| c.id}.include?(value)
          record.errors.add attr, "cannot be a descendant's id"
        end
      end
    end
  EOV
end